1.2.1 Systems software Flashcards
what is an operating system?
a collection of programs that work
together to provide an interface between the user and computer
what are the functions of an operating system?
- memory management
- resource management
- input/output management
- interrupt management
- security
- user interface
- utility software
what is paging?
when main memory is split physically into equal sections
what is segmentation?
when main memory is split logically into variable sizes
what are similarities between paging and segmentation?
-both used when RAM space is insufficient
-can cause disk thrashing
what is virtual memory?
a memory management technique that allows a computer to use a portion of it’s hard drive as if it were RAM
what is virtual memory used for?
-temporarily moves sections of programs not currently being used
-frees up memory for other programs in RAM
what is an interrupt?
an instruction that has high priority so it stops the current FDE cycle from being completed.
what are the stages of the interrupt
service routine (ISR)?
-interrupt register checked at the end of each FDE cycle
-if interrupt has a higher priority to the current instruction, the current contents of the registers in the CPU are transferred into a stack
-interrupt is completed using the FDE cycle
-interrupt register checked again
-if interrupts are of a higher priority, they will be put at the top of the stack to be completed first
-if there are no interrupts with a higher priority, the contents of the stack are popped and place back into the special memory registers
-the FDE cycle renews as before
what are the types of operating system?
-distributed
-real time
-multi-tasking
-multi-user
-embedded
what is a distributed operating system?
coordinates communication between many individual computers but it appears to be one system to the end user
what is an embedded operating system?
used in computers that serve a specific purpose
(washing machines)
what is a multi-tasking operating system?
manages the computer’s resources to provide the illusion to the user that it is possible to switch between tasks
(laptops- working on a document while listening to music)
(a single core computer can only run one application at a time, but the OS can switch between tasks quickly to make it look like multiple tasks are running simultaneously)
what is a multi-user operating system?
provides the facilities for multiple users to access the same system
(supercomputers)
what is a real-time operating system?
processes data within a guaranteed amount of time
(medical devices- heart rate monitors)
what are the functions of the BIOS (Basic Input Output System)?
-POST (Power On Self Test) which ensures that all hardware is correctly connected and functional
-checking the CPU clock, memory and processor
-testing for external memory devices
what is the use of a device driver?
enables the operating system to interact with hardware devices
what is a virtual machine?
a software-based computer that acts like a physical computer, but is only a digital representation of one
why are virtual machines used?
-testing programs
-protection from malware
-running software compatible with different versions and types of operating systems
what is scheduling?
allocating time slots for instructions to be completed
what are the types of scheduling?
-first come first served
-round robin
-shortest remaining time
-shortest job first
-multilevel feedback queue
what are the benefits of scheduling?
-increases efficiency
-reduces bottle neck
(instructions completed one at a time)
what is first come first served?
processes are completed in the order which the processor receives them
-simplest method to implement
-long wait times
what is round robin?
-processor time is divided equally among all running tasks (time slice)
-if process hasn’t finished when time slice is up, it stops running and the computer switches to the next process
-the suspended process will only resume running when it is next allocated processor time
-ensures every task is allocated processor time
-short wait times
-more processes running -> smaller time slice for each process, more urgent tasks are less likely to be completed quickly
what are benefits of round robin?
-ensures every task is allocated processor time
-short wait times
what are drawbacks of round robin?
-more processes running means smaller time slice for each process
-more urgent tasks are less likely to be completed quickly
what is shortest remaining time?
-the processes with the shortest time to completion go first
-until a different task is added with a shorter time to completion, which then takes priority
(different to the shortest job first as a long job which is mostly complete may have a very short time remaining, so it would prioritised)
what are benefits of shortest time remaining?
-reduced processing time
what are drawbacks of shortest time remaining?
-starvation
what is shortest job first?
the shortest instructions are completed first
-reduces wait times
-however can lead to starvation because longer instructions may not get completed
what are multilevel feedback queues?
-uses queues of tasks, where each queue has a different level of priority
-processes are chosen from different queues based on priority and how much processing time each process has already had
-initially, processes are added to a queue with a certain level of priority
-if a process uses too much CPU time, it is moved to a lower priority queue
-if a process has been idle for a long time, it is moved to a higher priority queue
-processes that depend on input/output devices require a lot of processing time, so they are kept in high priority queues
-processes that are quick to complete are served first
what are benefits of multi level feedback queues?
-all tasks are given processor time
(avoids starvation)
-more important jobs are dealt with sooner
-queues become more balanced the more tasks are processed, ensures no single high priority task dominate the processor’s time
what are drawbacks of multi level feedback queues?
-the most complex algorithm
-CPU intensive
